Bonds issued pursuant to this article shall be sold at a price of not less than par and accrued interest to the date of their respective deliveries. All bonds authorized by this article shall be sold at public sale, after public advertisement of the sale in a newspaper of general circulation in South Carolina or a financial journal published in the city of New York. The published notice shall appear not less than seven days prior to the occasion set for opening bids; provided, however, that any bonds issued hereunder may be sold at a private sale to the United States of America or any agency or department thereof.